Gay Marriage, Equal Protection, and Polygamy

Last night, I listened to a presentation on the struggle for same-sex marriage and how sweeping change would likely come, if it ever came at all.  The presenter explained that first the Defense of Marriage Act (a federal law defining marriage as between a man and a woman and exempting states from the full faith and credit clause in same-sex marriage cases) would need to either be repealed or struck down by the courts.  The justification for this would be that the Constitution does not give the federal government the power to regulate marriage and that the exemption from full faith and credit would violate the full faith and credit clause.

The presenter then went on to describe how the Supreme Court could strike down state bans on same-sex marriage by incoprorating the equal protection clause of the 14th Amendment.  While I am a proponent of same-sex marriage, I asked the presenter how, if the Court uses equal protection as its justification in forcing states to allow same-sex couples to marry, states could bar polygamous marriages.  I generally don't like this line of argument ("if you allow the gays to marry, soon you'll have polygamy and bestiality and on and on") and I don't think this logic would necessarily apply in cases where states are determining who can get married.  That is, if states are allowed to restrict marriage, one could argue for explanding it to same-sex couples while, for various reasons, barring multi-partner unions of the same kind.  But if the Supreme Court were to say that the "equal protection of the laws" means equal right to marry who you please (so long as they are consenting adults), I struggle to see how polygamous marriages could be exempt.

My professor stepped in at that point to point out what he thought was a key difference.  First, he referred to the fact that the "equal protection" justification has usually been applied to groups whose "differentness" is not based on any choice they made (race, gender, disability).  He reminded us that one of the key arguments for same-sex marriage opponents has been that they believe homosexuality to be a matter of choice and thus not subject to the same constitutional protections as race, gender, and disability.  Presumably, if the Court were to apply equal protection in terms of same-sex marriage, it would first have to find that homosexuality is not a choice.  And there, said the professor, would be where the line is drawn between same-sex marriage and polygamous marriages.  Same-sex attraction and love would be found to be "natural" and innate, while polygamous attraction and love would be defined as a choice, something unnatural.

That may be so, and the Court, if this were to happen, may fashion the rule in that way.  But is it true that polygamous love and attraction is unnatural or even, not beneficial?  Evolutionary biologists and psychologists would certainly argue that polyamorous relationships - and especially opposite-sex polyamorous relationships - can carry significant benefits for both men and women.  Many would also argue that same-sex polygamous relationships could be beneficial for many individuals .  Furthermore, who are the members of the Court to say what constitutes "real" love between a man and a woman, or between a man and two women, or two men and a woman, and so on?  In examining polygamous relationships, how would the Court suggest we go about determining whose love is genuine and whose love is just mere physical attraction?

As I said before, I don't actually think this should be used as a justification for banning same-sex marriage.  All I'm getting at is that if you use eaual protection to force states to allow it, how do you then turn around and say that those same protections should not apply to partnerships between more than two people?

I'd be interested in hearing what everyone thinks about this.